1. Field of the Invention
The present invention relates to a semiconductor integrated circuit with multiple power domains and, more particularly, to a domain power notification system that prevents erroneous data from being unknowingly received by one domain when another domain experiences a power condition.
2. Description of the Related Art
In a semiconductor integrated circuit that has multiple power domains that communicate with each other, an interruption in the power supply of a transmitting domain can lead to invalid data being received by a receiving domain. When the receiving domain is unaware that the transmitting domain is experiencing a power interruption, the receiving domain can unknowingly receive erroneous signals from the transmitting domain or random signals from the transmission line. In addition to Interruptions in the power supply, a low-voltage condition in the transmitting domain can also lead to invalid data being unknowingly received by the receiving domain.
For example, in a simple two-domain case, a semiconductor integrated circuit can have a 3.3V analog receive domain that receives and digitizes analog signals, and a 1.8V digital processing domain that processes the digitized signals from the analog receive domain. A lost power or low-voltage condition in the analog receive domain can lead to the digital processing domain unknowingly receiving invalid data.
Thus, there is a need for a technique that prevents a domain from unknowingly receiving invalid data when another domain loses power or enters a low-voltage condition.
The present invention provides a domain power notification system that detects when a domain experiences a power condition, and communicates that information to the domains that communicate with the problem domain. The effected domains stop communicating with the problem domain without passing erroneous information. The power conditions can include, for example, lost power and low-voltage conditions.
A domain power notification system in accordance with the present invention includes a plurality of power domains that receive a corresponding plurality of status signals, and output a corresponding plurality of power signals so that each power domain receives a corresponding status signal and outputs a corresponding power signal. Each domain is independently powered. The power signals represent power supply voltages on the power domains so that each power signal represents a power supply voltage on a power domain. Each power domain is connected to at least one other power domain.
The domain power notification system also includes a domain notification circuit that is connected to a first domain of the plurality of power domains. The domain notification circuit is independently-powered, receives a power signal from the first domain and a second power domain, and outputs a status signal to the first domain. The status signal indicates a power condition of the second power domain.
The present invention also includes a method of operating the domain notification circuit. In accordance with the present invention, the method includes the steps of monitoring a power signal from the second power domain and outputting a status signal to indicate when the power signal from the second power domain falls below a minimum operational voltage.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description and accompanying drawings that set forth an illustrative embodiment in which the principles of the invention are utilized.